Multipoint fixation implants

ABSTRACT

Bone anchor assemblies are disclosed herein that can provide for improved fixation as compared with traditional bone anchor assemblies. An exemplary assembly can include a bracket or wing that extends down from the receiver member and accommodates one or more auxiliary bone anchors that augment the fixation of the assembly&#39;s primary bone anchor. Another exemplary assembly can include a plate that is seated between the receiver member and the rod and accommodates one or more auxiliary bone anchors that augment the fixation of the assembly&#39;s primary bone anchor. Another exemplary assembly can include a hook that extends out from the receiver member to hook onto an anatomical structure or another implant to augment the fixation of the assembly&#39;s primary bone anchor. Surgical methods using the bone anchor assemblies described herein are also disclosed.

FIELD

Orthopedic implants and related methods are disclosed herein. For example, bone anchor assemblies with multiple bone engagement points are disclosed.

BACKGROUND

Bone anchor assemblies can be used in orthopedic surgery to fix bone during healing, fusion, or other processes. In spinal surgery, for example, bone anchor assemblies can be used to secure a spinal fixation element to one or more vertebrae to rigidly or dynamically stabilize the spine. Bone anchor assemblies can also be used as an engagement point for manipulating bone (e.g., distracting, compressing, or rotating one vertebra with respect to another vertebra, reducing fractures in a long bone, and so forth).

The integrity with which the bone anchor assembly engages the bone can affect the transfer of corrective biomechanical forces. While a great amount of care is exercised when placing bone anchor assemblies, it is common that a bone anchor assembly will be inserted in a compromised state. For example, the bone opening in which the assembly is disposed can be stripped (e.g., by driving the bone anchor assembly past its optimum holding position), the bone anchor assembly can be placed incorrectly (e.g., using an incorrect instrument maneuver such as an over-sized pilot hole), the bone anchor assembly can be placed outside of its intended trajectory (e.g., within a facet capsule or breached through a pedicle wall), or the bone anchor assembly can be inserted into compromised bone (e.g., bone that is fractured, osteoporotic, diseased, or otherwise lacking in structural integrity).

When the bone anchor assembly is in a compromised state, there can be sub-optimal purchase between the bone anchor assembly and the bone. The bone anchor assembly may feel unsecure to the surgeon, and it is possible that the bone anchor assembly could back out or become loosened over time. There are limited options for the surgeon when faced with these types of situations. In spinal surgery, for example, the surgeon can remove the bone anchor assembly and skip the vertebral level, though this can undesirably require expanding the surgical site to additional vertebral levels. The surgeon can remove and re-insert with a larger anchor, though this may not be an option when space for anchoring in the bone is limited. The surgeon can leave the compromised bone anchor assembly in place, which may be the safest alternative if the bone anchor assembly is in a safe location and attachment to the plate, rod, or other implant construct is definitive, as the additional compromised fixation may be better than removal.

Even when a bone anchor assembly is placed in a non-compromised state, the geometry of traditional bone anchor assemblies can limit the flexibility with which the bone attachment point can be located with respect to a plate, rod, or other implant construct coupled to the bone anchor assembly.

There is a continual need for improved bone anchor assemblies and related methods.

SUMMARY

Bone anchor assemblies are disclosed herein that can provide for improved fixation as compared with traditional bone anchor assemblies. An exemplary assembly can include a bracket or wing that extends down from the receiver member and accommodates one or more auxiliary bone anchors that augment the fixation of the assembly's primary bone anchor. Another exemplary assembly can include a plate that is seated between the receiver member and the rod and accommodates one or more auxiliary bone anchors that augment the fixation of the assembly's primary bone anchor. Another exemplary assembly can include a hook that extends out from the receiver member to hook onto an anatomical structure or another implant to augment the fixation of the assembly's primary bone anchor. Surgical methods using the bone anchor assemblies described herein are also disclosed.

In some embodiments, a bone anchor assembly includes a bone anchor; a receiver member coupled to a proximal end of the bone anchor and defining a recess configured to receive a rod; a closure mechanism threadably mated to the receiver member; a wing having a proximal portion disposed proximal to the receiver member, a distal portion that defines a bone anchor opening, and a spanning portion that connects the proximal and distal portions; and a nut configured to threadably engage the closure mechanism to secure the proximal portion of the wing to the proximal end of the receiver member.

The closure mechanism can be or can include a threaded post. The wing can include an opening through which at least a portion of the threaded post is disposed. The wing can be rotatable about the closure mechanism. A distal-facing surface of the proximal portion of the wing can bear against a proximal terminal end of the receiver member. A lateral surface of the distal portion of the wing can form a negative of a sidewall of the receiver member. A lateral surface of the spanning portion of the wing can form a negative of a sidewall of the receiver member. A lateral surface of the spanning portion of the wing can include a protrusion that engages a corresponding recess formed in the receiver member. The spanning portion can hug the sidewall of the receiver member. The receiver member can be polyaxially movable relative to the bone anchor. The assembly can include an auxiliary bone anchor disposed in the bone anchor opening of the distal portion of the wing. The proximal-most extent of the auxiliary bone anchor can be distal to a rod when the rod is disposed in the recess of the receiver member. The proximal-most extent of the auxiliary bone anchor can be distal to the distal-most extent of the receiver member. The spanning portion can have an adjustable height. The spanning portion can include first and second legs movable toward one another to increase the height of the spanning portion and movable away from one another to decrease the height of the spanning portion. The spanning portion can be deformable to allow the distal portion of the wing to be angled to match an abutting bone surface.

In some embodiments, a method of securing a bone anchor assembly to bone includes driving a bone anchor into bone, the bone anchor having a receiver member coupled to a proximal end thereof; positioning a rod in the receiver member; attaching a closure mechanism to the receiver member to retain the rod in the receiver member; coupling a proximal portion of a wing to at least one of the closure mechanism and a proximal surface of the receiver member; and inserting an auxiliary bone anchor through a bone anchor opening formed in a distal portion of the wing and driving the auxiliary bone anchor into the bone.

Coupling the proximal portion of the wing can include inserting at least a portion of the closure mechanism through an opening formed in the proximal portion of the wing. The method can include rotating the wing relative to receiver member to position the bone anchor opening of the wing with respect to a target location on the bone. The method can include deforming the wing to position the bone anchor opening of the wing with respect to a target location on the bone. The method can include adjusting a height of the wing such that the wing spans from the proximal-most extent of the receiver member to the bone. The bone anchor and the auxiliary bone anchor can be driven into a single vertebra.

In some embodiments, a bone anchor assembly includes a bone anchor; a receiver member coupled to a proximal end of the bone anchor and defining a recess configured to receive a rod; a closure mechanism threadably mated to the receiver member; a plate having a primary opening through which first and second arms of the receiver member extend, a bone anchor opening, and a saddle portion that extends across at least a portion of the primary opening such that the saddle portion is disposed in the recess of the receiver member; and an auxiliary bone anchor disposed through the bone anchor opening of the plate.

The assembly can include a rod disposed between the saddle portion of the plate and the closure mechanism. The saddle portion can be movably coupled to the plate. A distal facing surface of the saddle portion can form a section of a cylinder. The primary opening in the plate can be defined by a first sidewall. The bone anchor opening of the plate can be defined by a second sidewall. A height of the first sidewall can be reduced where the first sidewall meets the second sidewall. The assembly can include a cap configured to engage the first and second arms of the receiver member. The cap can define a central opening disposed proximal to a proximal-most extent of the receiver member. The central opening can receive at least a portion of the closure mechanism therethrough. The proximal-most extent of the auxiliary bone anchor can be distal to a rod when the rod is disposed in the recess of the receiver member. The proximal-most extent of the auxiliary bone anchor can be distal to the distal-most extent of the receiver member.

In some embodiments, a method of securing a bone anchor assembly to bone includes driving a bone anchor into bone, the bone anchor having a receiver member coupled to a proximal end thereof; inserting first and second arms of the receiver member through a primary opening of a plate such that a saddle portion of the plate is disposed in a rod-receiving recess of the receiver member; positioning a rod on a proximal-facing surface of the saddle portion such that the rod is disposed in the rod-receiving recess of the receiver member; attaching a closure mechanism to the receiver member to retain the rod in the receiver member; and inserting an auxiliary bone anchor through a bone anchor opening formed in the plate and driving the auxiliary bone anchor into the bone.

The method can include bending the plate to position the bone anchor opening against the bone. The method can include bending the saddle portion of the plate to position the bone anchor opening against the bone. The bone anchor and the auxiliary bone anchor can be driven into a single vertebra.

In some embodiments, a bone anchor assembly includes a bone anchor; a receiver member coupled to a proximal end of the bone anchor and defining a recess configured to receive a rod; a closure mechanism threadably mated to the receiver member; a plate having a primary opening through which at least a portion of the receiver member extends, a bone anchor opening, and a distal-facing portion that extends across a proximal-facing portion of the receiver member; and an auxiliary bone anchor disposed through the bone anchor opening of the plate.

In some embodiments, a bone anchor assembly includes a bone anchor; a receiver member coupled to a proximal end of the bone anchor and defining a recess configured to receive a rod; a closure mechanism threadably mated to the receiver member; and a hook having a body portion coupled to the receiver member and a curved extension projecting from the body portion.

The extension can be substantially U-shaped. The extension can define an inside curved surface and an outside curved surface. The inside curved surface can form a substantial negative of a lamina. The body portion can have a lateral sidewall that abuts a sidewall of the receiver member. The hook can be coupled to the receiver member by a collar. The collar can define a first opening in which the receiver member is disposed and a second opening through which a locking screw is disposed. The locking screw can threadably engage the body portion of the hook. The first opening can include an engagement feature that engages a corresponding engagement feature formed in or on an exterior of the receiver member. The second opening can have a tapered shape to pull the receiver member towards the body portion as the locking screw is tightened. The collar can be disposed proximal to a rod when the rod is disposed in the receiver member. The collar can extend around an outer periphery of the receiver member. The hook can be configured to pivot with the receiver member relative to the bone anchor. The hook can be coupled to the receiver member by a nut. The nut can be threaded onto the closure mechanism to compress a proximal portion of the hook against a proximal end of the receiver member.

In some embodiments, a method of securing a bone anchor assembly to bone includes driving a bone anchor into bone, the bone anchor having a receiver member coupled to a proximal end thereof; positioning a rod within a rod-receiving recess of the receiver member; attaching a hook to the receiver member and hooking an extension of the hook onto at least one of an anatomical structure and an implant; and attaching a closure mechanism to the receiver member to retain the rod in the receiver member.

The bone anchor can be driven into a first vertebra and the extension of the hook can be hooked onto a lamina of the first vertebra. The hook can be attached to the receiver member after the bone anchor is driven into the bone. The closure mechanism can be attached to the receiver member after the hook is attached to the receiver member. The hook can be attached to the receiver member after the rod is seated in the receiver member.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is an exploded perspective view of a prior art bone anchor assembly;

FIG. 1B is a sectional view of the bone anchor assembly of FIG. 1A;

FIG. 1C is a perspective view of the bone anchor assembly of FIG. 1A shown with extension tabs;

FIG. 2A is a perspective view of a bone anchor assembly and a spinal rod;

FIG. 2B is a perspective exploded view of the bone anchor assembly and spinal rod of FIG. 2A;

FIG. 2C is a perspective view of the bone anchor assembly and spinal rod of FIG. 2A;

FIG. 2D is a top view of the bone anchor assembly and spinal rod of FIG. 2A;

FIG. 2E is a perspective view of a wing of the bone anchor assembly of FIG. 2A;

FIG. 2F is another perspective view of a wing of the bone anchor assembly of FIG. 2A;

FIG. 2G is another perspective view of a wing of the bone anchor assembly of FIG. 2A;

FIG. 2H is another perspective view of a wing of the bone anchor assembly of FIG. 2A;

FIG. 2I is a perspective view of the bone anchor assembly and spinal rod of FIG. 2A, shown with an adjustable-height wing;

FIG. 2J is a perspective view of a wing of the bone anchor assembly of FIG. 2I;

FIG. 2K is another perspective view of a wing of the bone anchor assembly of FIG. 2I;

FIG. 2L is another perspective view of a wing of the bone anchor assembly of FIG. 2I;

FIG. 2M is another perspective view of a wing of the bone anchor assembly of FIG. 2I;

FIG. 3A is a perspective view of a bone anchor assembly and a spinal rod;

FIG. 3B is a perspective exploded view of the bone anchor assembly and spinal rod of FIG. 3A;

FIG. 3C is a perspective view of a plate of the bone anchor assembly of FIG. 3A;

FIG. 3D is another perspective view of a plate of the bone anchor assembly of FIG. 3A;

FIG. 3E is another perspective view of a plate of the bone anchor assembly of FIG. 3A;

FIG. 3F is another perspective view of a plate of the bone anchor assembly of FIG. 3A;

FIG. 3G is a perspective view of a receiver member and plate of the bone anchor assembly of FIG. 3A;

FIG. 3H is a perspective view of the bone anchor assembly and spinal rod of FIG. 3A, shown with a cap;

FIG. 3I is a perspective view of a human spine with the bone anchor assembly and spinal rod of FIG. 3A coupled thereto;

FIG. 4A is a perspective view of a bone anchor assembly and a spinal rod coupled to a human spine;

FIG. 4B is a perspective exploded view of the bone anchor assembly and spinal rod of FIG. 4A;

FIG. 4C is a perspective view of a hook of the bone anchor assembly of FIG. 4A;

FIG. 4D is a perspective view of the bone anchor assembly of FIG. 4A being assembled in situ; and

FIG. 4E is a perspective view of the bone anchor assembly of FIG. 4A shown with an alternate hook attachment.

DETAILED DESCRIPTION

Bone anchor assemblies are disclosed herein that can provide for improved fixation as compared with traditional bone anchor assemblies. An exemplary assembly can include a bracket or wing that extends down from the receiver member and accommodates one or more auxiliary bone anchors that augment the fixation of the assembly's primary bone anchor. Another exemplary assembly can include a plate that is seated between the receiver member and the rod and accommodates one or more auxiliary bone anchors that augment the fixation of the assembly's primary bone anchor. Another exemplary assembly can include a hook that extends out from the receiver member to hook onto an anatomical structure or another implant to augment the fixation of the assembly's primary bone anchor. Surgical methods using the bone anchor assemblies described herein are also disclosed.

Certain exemplary embodiments will now be described to provide an overall understanding of the principles of the structure, function, manufacture, and use of the systems and methods disclosed herein. One or more examples of these embodiments are illustrated in the accompanying drawings. Those skilled in the art will understand that the systems and methods specifically described herein and illustrated in the accompanying drawings are non-limiting exemplary embodiments. The features illustrated or described in connection with one exemplary embodiment may be combined with the features of other embodiments..

Prior Art Bone Anchor Assembly

FIGS. 1A-1C illustrate a prior art bone anchor assembly 100 with various features that can be included in the bone anchor assemblies 200, 300, 400 described below. It will be appreciated that the illustrated bone anchor assembly 100 is exemplary and that the bone anchor assemblies 200, 300, 400 can include additional or alternative features.

The illustrated bone anchor assembly 100 includes a bone anchor 102, a receiver member 104 for receiving a spinal fixation element, such as a spinal rod 106, to be coupled to the bone anchor 102, and a closure mechanism 108 to capture a spinal fixation element within the receiver member and fix the spinal fixation element with respect to the receiver member. The bone anchor 102 includes a proximal head 110 and a distal shaft 112 configured to engage bone. The receiver member 104 has a proximal end having a pair of spaced apart arms 114A, 114B defining a recess 116 therebetween and a distal end having a distal end surface defining an opening through which at least a portion of the bone anchor 102 extends. The closure mechanism 108 can be positionable between and can engage the arms 114A, 114B to capture a spinal fixation element, e.g., a spinal rod 106, within the receiver member 104 and fix the spinal fixation element with respect to the receiver member.

The proximal head 110 of the bone anchor 102 is generally in the shape of a truncated sphere having a planar proximal surface and an approximately spherically-shaped distal surface. The illustrated bone anchor assembly 100 is a polyaxial bone screw designed for posterior implantation in the pedicle or lateral mass of a vertebra. The proximal head 110 of the bone anchor 102 engages the distal end of the receiver member 104 in a ball and socket like arrangement in which the proximal head and the distal shaft 112 can pivot relative to the receiver member. The distal surface of the proximal head 110 of the bone anchor 102 and a mating surface within the distal end of the receiver member 104 can have any shape that facilitates this arrangement, including, for example, spherical (as illustrated), toroidal, conical, frustoconical, and any combinations of these shapes.

The distal shaft 112 of the bone anchor 102 can be configured to engage bone and, in the illustrated embodiment, includes an external bone engaging thread. The thread form for the distal shaft 112, including the number of threads, the pitch, the major and minor diameters, and the thread shape, can be selected to facilitate connection with bone. Exemplary thread forms are disclosed in U.S. Patent Application Publication No. 2011/0288599, filed on May 18, 2011, and in U.S. Patent Application Publication No. 2013/0053901, filed on Aug. 22, 2012, both of which are hereby incorporated by reference herein. The distal shaft 112 can also include other structures for engaging bone, including a hook. The distal shaft 112 of the bone anchor 102 can be cannulated, having a central passage or cannula extending the length of the bone anchor to facilitate delivery of the bone anchor over a guidewire in, for example, minimally-invasive procedures. Other components of the bone anchor assembly 100, including, for example, the closure mechanism 108, the receiver member 104, and the compression member or cap 118 (discussed below) can be cannulated or otherwise have an opening to permit delivery over a guidewire. The distal shaft 112 can also include one or more sidewall openings or fenestrations that communicate with the cannula to permit bone in-growth or to permit the dispensing of bone cement or other materials through the bone anchor 102. The sidewall openings can extend radially from the cannula through the sidewall of the distal shaft 112. Exemplary systems for delivering bone cement to the bone anchor assembly 100 and alternative bone anchor configurations for facilitating cement delivery are described in U.S. Patent Application Publication No. 2010/0114174, filed on Oct. 29, 2009, which is hereby incorporated by reference herein. The distal shaft 112 of the bone anchor 102 can also be coated with materials to permit bone growth, such as, for example, hydroxyapatite, and the bone anchor assembly 100 can be coated partially or entirely with anti-infective materials, such as, for example, tryclosan.

The proximal end of the receiver member 104 includes a pair of spaced apart arms 114A, 114B defining a U-shaped recess 116 therebetween for receiving a spinal fixation element, e.g., a spinal rod 106. Each of the arms 114A, 114B can extend from the distal end of the receiver member 104 to a free end. The outer surfaces of each of the arms 114A, 114B can include a feature, such as a recess, dimple, notch, projection, or the like, to facilitate connection of the receiver member 104 to instruments. For example, the outer surface of each arm 114A, 114B can include an arcuate groove at the respective free end of the arms. Such grooves are described in more detail in U.S. Pat. No. 7,179,261, issued on Feb. 20, 2007, which is hereby incorporated by reference herein.

The distal end of the receiver member 104 includes a distal end surface which is generally annular in shape defining a circular opening through which at least a portion of the bone anchor 102 extends. For example, the distal shaft 112 of the bone anchor 102 can extend through the opening.

The bone anchor 102 can be selectively fixed relative to the receiver member 104. Prior to fixation, the bone anchor 102 is movable relative to the receiver member 104 within a cone of angulation generally defined by the geometry of the distal end of the receiver member and the proximal head 110 of the bone anchor 102. The bone anchor assembly 100 can be a favored angle screw, for example as disclosed in U.S. Pat. No. 6,974,460, issued on Dec. 13, 2005, and in U.S. Pat. No. 6,736,820, issued on May 18, 2004, both of which are hereby incorporated by reference herein. Alternatively, the bone anchor assembly 100 can be a conventional (non-biased) polyaxial screw in which the bone anchor 102 pivots in the same amount in every direction.

The spinal fixation element, e.g., the spinal rod 106, can either directly contact the proximal head 110 of the bone anchor 102 or can contact an intermediate element, e.g., a compression member 118. The compression member 118 can be positioned within the receiver member 104 and interposed between the spinal rod 106 and the proximal head 110 of the bone anchor 102 to compress the distal outer surface of the proximal head into direct, fixed engagement with the distal inner surface of the receiver member 104. The compression member 118 can include a pair of spaced apart arms 120A and 120B defining a U-shaped seat 122 for receiving the spinal rod 106 and a distal surface for engaging the proximal head 110 of the bone anchor 102.

The proximal end of the receiver member 104 can be configured to receive a closure mechanism 108 positionable between and engaging the arms 114A, 114B of the receiver member. The closure mechanism 108 can be configured to capture a spinal fixation element, e.g., a spinal rod 106, within the receiver member 104, to fix the spinal rod relative to the receiver member, and to fix the bone anchor 102 relative to the receiver member. The closure mechanism 108 can be a single set screw having an outer thread for engaging an inner thread provided on the arms 114A, 114B of the receiver member 104. In the illustrated embodiment, however, the closure mechanism 108 includes an outer set screw 124 operable to act on the compression member 118 and an inner set screw 126 operable to act on the rod 106. The receiver member 104 can include, can be formed integrally with, or can be coupled to one or more extension tabs 128 (shown in FIG. 1C) that extend proximally from the receiver member 104 to functionally extend the length of the arms 114A, 114B. The extension tabs 128 can facilitate installation and assembly of a fixation or stabilization construct and can be removed prior to completing a surgical procedure.

The bone anchor assembly 100 can be used with a spinal fixation element such as rigid spinal rod 106. Alternatively, the spinal fixation element can be a dynamic stabilization member that allows controlled mobility between the instrumented vertebrae.

In use, the bone anchor assembly 100 can be assembled such that the distal shaft 112 extends through the opening in the distal end of the receiver member 104 and the proximal head 110 of the bone anchor 102 is received in the distal end of the receiver member 104. A driver instrument can be fitted with the bone anchor 102 to drive the bone anchor into bone. The compression member 118 can be positioned within the receiver member 104 such that the arms 120A, 120B of the compression member are aligned with the arms 114A, 114B of the receiver member 104 and the lower surface of the compression member 118 is in contact with the proximal head 110 of the bone anchor 102. A spinal fixation element, e.g., the spinal rod 106, can be located in the recess 116 of the receiver member 104. The closure mechanism 108 can be engaged with the inner thread provided on the arms 114A, 114B of the receiver member 104. A torsional force can be applied to the outer set screw 124 to move it within the recess 116 so as to force the compression member 118 onto the proximal head 110 of the bone anchor 102, thereby locking the angular position of the bone anchor 102 relative to the receiver member 104. A torsional force can be applied to the inner set screw 126 to force the spinal rod 106 into engagement with the compression member 118 and thereby fix the spinal rod 106 relative to the receiver member 104.

The bone anchor assemblies 200, 300, 400 described below can be configured to operate in conjunction with, or can include any of the features of, bone anchor assemblies of the type described above or other types known in the art. Exemplary bone anchor assemblies include monoaxial screws, polyaxial screws, uniplanar screws, favored-angle screws, and/or any of a variety of other bone anchor types known in the art. Further information on favored-angle screws can be found in U.S. Patent Application Publication No. 2013/0096618, filed on Oct. 9, 2012, which is hereby incorporated by reference herein.

Multipoint Fixation Implants

FIGS. 2A-2M illustrate an exemplary embodiment of a bone anchor assembly 200, shown with a spinal rod 206. As noted above, a bone anchor can sometimes be inserted in a compromised state. This can be undesirable, especially in the cervical region of the spine where there is limited bone area in which to install additional bone anchors. The illustrated bone anchor assembly 200 can allow for supplemental fixation of a primary bone anchor in a compact footprint, without necessarily requiring removal or re-insertion of the primary bone anchor. As shown, the bone anchor assembly 200 can include a bone anchor 202, a receiver member 204, a closure mechanism 208, a bracket or wing 230, a nut 232, and one or more auxiliary bone anchors 234. In use, the wing 230 can be secured to the receiver member 204, e.g., using the closure mechanism 208 and nut 232, thereby providing the ability to augment fixation of the bone anchor 202 with the one or more auxiliary bone anchors 234.

Except as described below or as will be readily appreciated by one having ordinary skill in the art, the bone anchor 202 and receiver member 204 are substantially similar to the bone anchor 102 and receiver member 104 described above. A detailed description of the structure and function thereof is thus omitted here for the sake of brevity. The bone anchor assembly 200 can include any one or more of the features of the bone anchor assembly 100 described above.

The closure mechanism 208 can be selectively secured to the receiver member 204 to capture a spinal fixation element, e.g., a spinal rod 206, within the receiver member. Tightening or locking the closure mechanism 208 can be effective to fix the spinal rod 206 relative to the receiver member 204, and to fix an angular position of the bone anchor 202 relative to the receiver member 204. The illustrated closure mechanism 208 is in the form of a threaded post with an enlarged-diameter distal portion 208 d and a reduced-diameter proximal portion 208 p. In other embodiments, the proximal and distal portions 208 p, 208 d can have the same diameter, or the proximal portion can have a diameter greater than that of the distal portion. The distal portion 208 d of the closure mechanism 208 can be threaded into the receiver member 204 to engage a spinal rod 206 disposed in the receiver member. The proximal portion 208 p of the closure mechanism 208 can protrude above the receiver member 204, e.g., above a proximal-facing terminal end surface of the receiver member, and through an opening 236 formed in the wing 230, as described further below.

In the illustrated embodiment, the closure mechanism 208 bears directly against the spinal rod 206, which in turn bears directly against the head of the bone anchor 202. It will be appreciated, however, that one or more intermediate elements can also be included in the bone anchor assembly 200. For example, the bone anchor assembly 200 can include a compression member of the type described above disposed between the spinal rod 206 and the head of the bone anchor 202. The closure mechanism 208 can be a single set screw as shown, or can include an outer set screw operable to act on a compression member and an inner set screw operable to act on the rod 206. The closure mechanism 208 can include a driving interface (e.g., torx, flathead, Phillips head, square, or otherwise) to facilitate rotational advancement or retraction of the closure mechanism relative to the receiver member 204 using a driver instrument.

The nut 232 can include a central opening 238 sized to receive at least a portion of the proximal end 208 p of the closure mechanism 208 therethrough. The central opening 238 can include an internal thread that corresponds to the external thread of the closure mechanism 208, such that the nut 232 can be threaded onto the closure mechanism and tightened to secure the wing 230 to the closure mechanism and the receiver member 204 in which the closure mechanism is disposed. The outer surface of the nut 232 can be faceted or otherwise configured to facilitate application of torque to the nut. In some embodiments, the nut 232 can have a hexagonal or square cross-section.

As shown in FIGS. 2E-2H, the bracket or wing 230 can include a proximal portion 230 p that can contact the receiver member 204, a distal portion 230 d that can contact a bone surface or be disposed in close proximity to a bone surface, and a spanning portion 230 s that connects the proximal and distal portions.

The proximal portion 230 p of the wing 230 can include a central opening 236 sized to receive at least a portion of the closure mechanism 208 therethrough. For example, the central opening 236 can be sized to receive the proximal portion 208 p of the closure mechanism 208 therethrough. The central opening 236 can include a smooth, non-threaded interior surface to allow the wing 230 and the closure mechanism 208 to be freely rotatable with respect to one another. A proximal-facing surface 240 of the proximal portion 230 p of the wing 230 can be domed or rounded to provide an atraumatic surface and reduce the risk of tissue irritation post-implantation. A distal-facing surface 242 of the proximal portion 230 p of the wing 230 can be configured to engage the proximal-facing surface of the receiver member 204. The distal-facing surface 242 can form a negative or a substantial negative of the proximal-facing surface of the receiver member 204. For example, the proximal-facing surfaces of the arms 214A, 214B of the receiver member 204 can be radially-convex, and the distal-facing surface 242 of the wing 230 can define a radially-concave channel that receives the convex ends of the arms. In some embodiments, the central opening 236 or another feature of the wing 230 can be sized and configured to snap onto or capture a portion of the closure mechanism 208 or a proximal surface of the receiver member 204.

The distal portion 230 d of the wing 230 can include one or more openings 244 configured to receive a bone anchor 234 therethrough. While two bone anchor openings 244 are shown in the illustrated embodiment, it will be appreciated that the wing 230 can include any number of bone anchor openings (e.g., one, two, three, four, five, and so on). The bone anchor openings 244 can include any of a number of features for accepting bone anchors 234 at varying angles and/or increasing the security and stability with which bone anchors can be secured to the wing 230. Exemplary features that can be included are disclosed in U.S. Pat. No. 7,637,928, issued on Dec. 29, 2009; U.S. Pat. No. 8,343,196, issued on Jan. 1, 2013; U.S. Pat. No. 8,574,268, issued on Nov. 5, 2013; U.S. Pat. No. 8,845,697, issued on Sep. 30, 2014; and U.S. Pat. No. 8,758,346, issued on Jun. 24, 2014, which are each hereby incorporated by reference herein. For example, the bone anchor openings 244 can be at least partially threaded to receive a variable-angle locking screw having a threaded proximal head. As shown, the openings 244 can have a plurality of columns of threads spaced apart to define a plurality of non-threaded recesses. In the illustrated embodiment, each of the openings 244 has four columns of threads. The columns of threads can be arranged around the inner surface of each of the openings 244 for engaging threads on the heads of locking auxiliary bone anchors and/or variable-angle locking auxiliary bone anchors. The auxiliary bone anchors 234 can thus be locked with the wing 230 coaxially with the central axis of the opening 244 or at a selected angle within a range of selectable angles relative to the central axis of the opening. The auxiliary bone anchors 234 can include features to facilitate this variable-angle locking, such as a proximal head that is at least partially spherical having a thread with a profile that follows the arc-shaped radius of curvature of the spherical portion of the head. The variable-angle capability of the screw/opening interface can allow the user to place locking auxiliary bone anchors into the bone at any angle within defined angulation limits, thus providing improved placement flexibility and eliminating or reducing the need to conform the distal portion of the wing to the bone surface to achieve a desired insertion angle. The auxiliary bone anchors 234 can be driven into the bone with diverging or converging longitudinal axes (relative to each other and/or relative to the primary bone anchor 202) which can provide improved resistance to pullout. In some embodiments, the interior surfaces of the openings 244 can be smooth or spherical, without threads or locking features.

The central axis of each of the openings 244 can be perpendicular or substantially perpendicular to a distal-facing surface 246 of the wing 230. Alternatively, one or more of the openings can have a central axis that extends at an oblique angle with respect to the distal-facing surface 246. In the illustrated embodiment, the central axis of each opening 244 extends at an angle of about 7 degrees with respect to the distal-facing surface 246. In some embodiments, the central axis of each opening 244 can extend at an angle of between about 0 degrees and about 15 degrees with respect to the distal-facing surface 246 (e.g., embodiments used for bony attachment locations that allow direct proximal to distal screw insertion). In some embodiments, the central axis of each opening 244 can extend at an angle of between about 15 degrees and about 45 degrees with respect to the distal-facing surface 246 (e.g., embodiments used for bony attachment locations where an angled trajectory may avoid or target specific anatomy). Angled or divergent central axes can advantageously increase the pullout resistance of the construct.

The distal portion 230 d of the wing 230 can have a distal-facing surface 246 configured to contact bone or to be disposed in close proximity to bone. The distal-facing surface 246 can include teeth, texturing, or other surface features to enhance grip with the adjacent bone. The distal portion 230 d of the wing 230 can have a lateral surface 248 that abuts a sidewall of the receiver member 204. The lateral surface 248 can form a negative of the sidewall of the receiver member 204, such that the distal-portion 230 d of the wing 230 can hug the receiver member with minimal or zero gap therebetween. For example, the lateral surface 248 can be concave with a radius of curvature equal or substantially equal to a radius of curvature of the exterior sidewall of the receiver member 204.

The spanning portion 230 s of the wing 230 can extend vertically in a proximal-distal direction to join the proximal portion 230 p of the wing to the distal portion 230 d of the wing. The spanning portion 230 s of the wing 230 can have a lateral surface 250 that engages a sidewall of the receiver member 204. The lateral surface 250 can form a negative of the sidewall of the receiver member 204, such that the spanning portion 230 s of the wing 230 can hug the receiver member with minimal or zero gap therebetween. For example, the lateral surface 250 can be concave with a radius of curvature equal or substantially equal to a radius of curvature of the exterior sidewall of the receiver member 204. The lateral surface 250 can also include one or more protrusions 252 for engaging a corresponding recess 254 formed in the sidewall of the receiver member 204, or one or more recesses in which a protrusion of the receiver member is received. The interaction between the one or more protrusions 252 and the one or more recesses 254 can be effective to limit or prevent rotation of the wing 230 with respect to the receiver member 204. This interaction can also be effective to limit or prevent movement of the wing 230 with respect to the receiver member 204 along a proximal-distal axis. The spanning portion 230 s can include webbing or ribs 256 to enhance the structural rigidity of the wing 230. The ribs 256 can be formed in an outer surface of the spanning portion 230 s, opposite to the lateral surface 250 that engages the receiver member 204.

The proximal portion 230 p, distal portion 230 d, and spanning portion 230 s can be formed integrally as a monolithic unit as shown, or one or more of said components can be separate and selectively attachable to the others. In some embodiments, a kit of modular components can be provided to allow selection of the components most appropriate for a given use. For example, a spanning portion 230 s of appropriate height can be selected based on the distance between the proximal end of the receiver member 204 and the bone surface in a given application.

One or more portions of the wing 230 can be flexible or deformable to allow the wing to be custom-tailored for a particular situation.

For example, the distal portion 230 d of the wing 230 can be flexible or deformable to allow the distal portion to be contoured to the bone surface. The distal portion 230 d can be contoured before implantation or in situ. The distal portion 230 d can be contoured using a separate bending instrument, or by tightening the bone anchors 234 to deform the distal portion into intimate contact with the bone surface. The distal portion 230 d of the wing 230 can be pre-shaped or pre-contoured, e.g., during manufacture, to match a bone surface with which the bone anchor assembly 200 is to be used.

By way of further example, the spanning portion 230 s of the wing 230 can be flexible or deformable to allow the position of the bone anchor openings 244 to be adjusted relative to the receiver member 204. The spanning portion 230 s can be bent or flexed inwardly or outwardly (e.g., in a medial-lateral direction) to move the bone anchor openings 244 inward towards the receiver member 204 or outward away from the receiver member. Such bending can also increase or decrease the effective height of the wing 230, to accommodate varying distances that may be encountered between the proximal end of the receiver member 204 and the bone surface. The spanning portion 230 s can be bent or flexed up or down (e.g., in a superior-inferior direction) to move the bone anchor openings 244 relative to the receiver member 204. The spanning portion 230 s can be contoured before implantation or in situ. The spanning portion 230 s can be contoured using a separate bending instrument, or by tightening the bone anchors 234 to deform the spanning portion into the desired shape. The spanning portion 230 s of the wing 230 can be pre-shaped or pre-contoured, e.g., during manufacture, for a given application.

As yet another example, the proximal portion 230 p of the wing 230 can be flexible or deformable, and/or the connections or locations at which the proximal portion 230 p, the distal portion 230 d, and the spanning portion 230 s are joined can be flexible or deformable. The proximal portion 230 p, distal portion 230 d, and spanning portion 230 s can be joined by a living hinge or other joint to allow adjustment to their relative positions.

The spanning portion 230 s can have an adjustable height. For example, as shown in FIGS. 2I-2M, the spanning portion 230 s can include first and second flexible or deformable legs 258. By bending the legs 258 inward towards one another, the height of the spanning portion 230 s can be increased. By bending the legs 258 outward away from one another, the height of the spanning portion 230 s can be decreased. Each leg 258 can include an upper portion and a lower portion joined by a flexible joint (e.g., a living hinge, pivot pin, or the like). Rounded or semi-circular surfaces can be formed at the connections between the legs 258 and the proximal and distal portions 230 p, 230 d of the wing 230 to reduce material stress as the legs are bent. Similarly, a rounded or semi-circular cut-out can be formed where the upper portion of each leg 258 meets the lower portion. The cut-out can reduce stress and also provide an engagement surface for gripping the legs 258 with a tool configured to apply a squeezing force thereto.

The bone anchor assembly 200 can provide significant flexibility for the surgeon. The wing 230 can be easily flipped around to be positioned on either side of the rod 206 (e.g., on a medial side or a lateral side of the rod). The wing 230 can be freely rotated about the closure mechanism 208 prior to final locking of the wing to the receiver member 204, allowing the auxiliary bone anchor holes 244 to be positioned at various locations with respect to the spinal rod 206, as shown in FIG. 2D. As described in detail above, the wing 230 can be deformable or flexible, or can include deformable or flexible portions, to allow the wing to fit snugly with the receiver member 204, to match a contour of the bone surface, to reposition the auxiliary bone anchor holes 244 with respect to the receiver member, and/or to adjust a height of the wing to accommodate receiver members of different heights or situations where the primary bone anchor 202 is over or under inserted into the bone.

Referring again to FIG. 2A, the proximal-most extent of each auxiliary bone anchor 234 can be distal to the spinal rod 206. In other embodiments, the proximal-most extent of each auxiliary bone anchor 234 can be distal to the distal-most extent of the receiver member 204. These configurations can advantageously reduce the overall profile of the assembly 200. The wing 200 can be Z-shaped or substantially Z-shaped.

The wing 230 can extend radially outward from the receiver member 204 (e.g., by a distance equal to the width of the distal portion 230 d of the wing). The degree to which the wing 230 extends outward from the receiver member 204 can vary among different embodiments. In the illustrated embodiment, the ratio of wing extension to rod diameter (or the ratio of wing extension to the width of the rod-receiving recess in the receiver member) is about 2:1. In some embodiments, this ratio can be less than about 10:1, less than about 5:1, less than about 3:1, less than about 2:1, less than about 1:1, and/or less than about 0.5:1. In some embodiments, the ratio can be about 10:1, about 5:1, about 3:1, about 2:1, about 1:1, or about 0.5:1.

The centers of the auxiliary bone anchor holes 244 (and thus at least a portion of the auxiliary bone anchors 234 disposed therein) can be spaced radially apart from the center of the opening in the receiver member 204 in which the primary bone anchor 202 is disposed. In some embodiments, this spacing can be less than about 2.5 times the diameter of the receiver member 204. In some embodiments, this spacing can be less than about 2 times the diameter of the receiver member 204. In some embodiments, this spacing can be less than the diameter of the receiver member 204. In some embodiments, this spacing can be between about 5 mm and about 10 mm. In some embodiments, this spacing can be about 7.5 mm. In some embodiments, the auxiliary bone anchors 234 can be contained within an envelope no bigger than 2.5 times the diameter of the receiver member 204. In some embodiments, the auxiliary bone anchors 234 can be contained within an envelope no bigger than 2 times the diameter of the receiver member 204.

The auxiliary bone anchors 234 can include any of the features of the bone anchor 202 described above, and any of a variety of other bone screws or other anchors can be used instead or in addition. As noted above, the auxiliary bone anchors 234 can have threaded proximal heads to facilitate variable-angle locking with the wing 230. In some embodiments, the auxiliary bone anchors 234 can have a length of about 6 mm to about 20 mm (e.g., in embodiments used for cervical applications). In some embodiments, the auxiliary bone anchors 234 can have a length of about 6 mm to about 100 mm (e.g., in embodiments used for lumbar or sacral applications). The length of the auxiliary bone anchors 234 can be selected based on various factors, including the available safe bone at any given attachment location. The auxiliary bone anchors 234 can have a length equal to that of the primary bone anchor 202. The auxiliary bone anchors 234 can have a length less than that of the primary bone anchor 202. The auxiliary bone anchors 234 can have a length that is between about 60% and about 80% of the length of the primary bone anchor 202. The auxiliary bone anchors 234 can have a length that is about 70% of the length of the primary bone anchor 202. The auxiliary bone anchors 234 can have a length of about 10 mm. The auxiliary bone anchors 234 can have a length of about 14 mm. In some embodiments, two 10 mm auxiliary bone anchors can be used with one 14 mm primary bone anchor. In some embodiments, one 14 mm auxiliary bone anchor can be used with one 14 mm primary bone anchor. The auxiliary bone anchors 234 can have a shank diameter equal to that of the primary bone anchor 202. The auxiliary bone anchors 234 can have a shank diameter less than that of the primary bone anchor 202. The auxiliary bone anchors 234 can have a shank diameter that is between about 50% and about 70% of the shank diameter of the primary bone anchor 202. The auxiliary bone anchors 234 can have a shank diameter that is about 60% of the shank diameter of the primary bone anchor 202.

FIGS. 3A-3I illustrate an exemplary embodiment of a bone anchor assembly 300, shown with a spinal rod 306. As shown ,the bone anchor assembly 300 can include a bone anchor 302, a receiver member 304, a closure mechanism 308, a grommet or plate 360, and one or more auxiliary bone anchors 334. In use, a saddle portion of the plate can be disposed between the rod 306 and the receiver member 304 to secure the plate 360 to the receiver member, thereby providing the ability to augment fixation of the bone anchor 302 with the one or more auxiliary bone anchors 334.

Except as described below or as will be readily appreciated by one having ordinary skill in the art, the bone anchor 302, receiver member 304, and closure mechanism 308 are substantially similar to the bone anchor 102, receiver member 104, and closure mechanism 108 described above. A detailed description of the structure and function thereof is thus omitted here for the sake of brevity. The bone anchor assembly 300 can include any one or more of the features of the bone anchor assembly 100 described above.

As shown in FIGS. 3C-3F, the grommet or plate 360 can include a primary opening 362 configured to receive at least a portion of the receiver member 304 therethrough. The plate can also include one or more openings 364 configured to receive a bone anchor 334 therethrough. While a single bone anchor opening 364 is shown in the illustrated embodiment, it will be appreciated that the plate 360 can include any number of bone anchor openings (e.g., one, two, three, four, five, and so on). The bone anchor openings 364 can include any of a number of features for accepting bone anchors 334 at varying angles and/or increasing the security and stability with which bone anchors can be secured to the plate 360. Exemplary features that can be included are disclosed in U.S. Pat. No. 7,637,928, issued on Dec. 29, 2009; U.S. Pat. No. 8,343,196, issued on Jan. 1, 2013; U.S. Pat. No. 8,574,268, issued on Nov. 5, 2013; U.S. Pat. No. 8,845,697, issued on Sep. 30, 2014; and U.S. Pat. No. 8,758,346, issued on Jun. 24, 2014, which are each hereby incorporated by reference herein. For example, the bone anchor opening 364 can be at least partially threaded to receive a variable-angle locking screw having a threaded proximal head. As shown, the opening 364 can have a plurality of columns of threads spaced apart to define a plurality of non-threaded recesses. In the illustrated embodiment, the opening 364 has four columns of threads. The columns of threads can be arranged around the inner surface of the opening 364 for engaging threads on the heads of locking auxiliary bone anchors and/or variable-angle locking auxiliary bone anchors. The auxiliary bone anchor 334 can thus be locked with the plate 360 coaxially with the central axis of the opening 364 or at a selected angle within a range of selectable angles relative to the central axis of the opening. The auxiliary bone anchor 334 can include features to facilitate this variable-angle locking, such as a proximal head that is at least partially spherical having a thread with a profile that follows the arc-shaped radius of curvature of the spherical portion of the head. The variable-angle capability of the screw/opening interface can allow the user to place locking auxiliary bone anchors into the bone at any angle within defined angulation limits, thus providing improved placement flexibility and eliminating or reducing the need to conform the plate to the bone surface to achieve a desired insertion angle. The auxiliary bone anchor 334 can be driven into the bone with a diverging or converging longitudinal axis relative to the primary bone anchor 302 and/or relative to other auxiliary bone anchors 334, which can provide improved resistance to pullout. In some embodiments, the interior surface of the opening 334 can be smooth or spherical, without threads or locking features.

The central axis of the opening 364 can be perpendicular or substantially perpendicular to a distal-facing surface of the plate 360. Alternatively, the opening 364 can have a central axis that extends at an oblique angle with respect to the distal-facing surface. In the illustrated embodiment, the central axis of the opening 364 extends at an angle of about 0 degrees with respect to the distal-facing surface. In some embodiments, the central axis of the opening 364 can extend at an angle of between about 0 degrees and about 15 degrees with respect to the distal-facing surface (e.g., embodiments used for bony attachment locations that allow direct proximal to distal screw insertion). In some embodiments, the central axis of the opening 364 can extend at an angle of between about 15 degrees and about 45 degrees with respect to the distal-facing surface (e.g., embodiments used for bony attachment locations where an angled trajectory may avoid or target specific anatomy). An angled or divergent central axis can advantageously increase the pullout resistance of the construct.

The plate 360 can include a saddle portion 366 that extends across at least a portion of the primary opening 362. The saddle portion 366 can span entirely across the primary opening 362, or can be cantilevered as shown to project out across the opening without contacting the opposite side of the opening. The latter configuration can advantageously facilitate bending of the saddle portion 366 with respect to the rest of the plate 360, thereby allowing the position of the plate with respect to the receiver member 304 to be adjusted (e.g., to bend the plate down into contact with the bone surface). The saddle portion 366 can include a distal facing surface 366 d that mimics the distal facing surface of a spinal fixation or stabilization element with which the bone anchor assembly 300 is to be used. For example, in the case of a cylindrical spinal rod 306, the distal-facing surface 366 d of the saddle portion 366 can define a section of a cylinder having a radius equal to or substantially equal to the diameter of the spinal rod. The proximal-facing surface 366 p of the saddle portion 366 can define a seat configured to receive the spinal fixation or stabilization element therein. In the illustrated embodiment, the seat 366 p is sized and shaped to receive a cylindrical spinal rod 306 therein. The radius of curvature of the proximal-facing seat 366 p can be equal to or substantially equal to that of the rod-receiving channel of the receiver member 304.

The saddle portion 366 can effectively divide the primary opening 362 into first and second openings on either side of the saddle portion, each sized to receive a corresponding one of the arms 314A, 314B of the receiver member 304. When assembled, the opposed arms 314A, 314B of the receiver member can be inserted through the first and second openings such that the plate 360 surrounds the receiver member 304 and such that the saddle portion 366 is seated within the rod-receiving recess of the receiver member. The spinal rod 306 can then be seated on the proximal-facing surface 366 p of the saddle portion 366, between the opposed arms 314A, 314B of the receiver member 304, and locked in place with the closure mechanism 308 as described above, thereby also locking the plate 360 to the receiver member. An auxiliary bone anchor 334 can be inserted through each of the one or more bone anchor openings 364 in the plate to augment the fixation provided by the primary bone anchor 302.

The primary opening 362 in the plate can be defined by a first sidewall 368 that is generally ring-shaped and that intersects with a second sidewall 370 that is also generally ring-shaped and that defines the one or more auxiliary bone anchor openings 364. The height of the first sidewall 368 can be reduced at the junction with the second sidewall 370 or in areas adjacent thereto to facilitate bending of the plate 360 to reposition the auxiliary bone anchor opening 364 with respect to the receiver member 304.

The first and second sidewalls 368, 370 can be formed integrally as a monolithic unit as shown, or one or more of said components can be separate and selectively attachable to the other. In some embodiments, a kit of modular components can be provided to allow selection of the components most appropriate for a given use. For example, a first sidewall 368 of appropriate size can be selected based on the size of the receiver member 304 or the size of the spinal rod 306. By way of further example, one or more modular second sidewalls 370 can be attached to the first sidewall 368, e.g., depending on the number of auxiliary bone anchors 334 that are to be used.

The second sidewall 370, and thus the auxiliary bone anchor opening 364 defined thereby, can be positioned at any of a variety of locations about the perimeter of the first sidewall 368. In the illustrated embodiment, for example, the auxiliary bone anchor opening 364 is positioned approximately at a “5 o'clock” or “lower” position with respect to the saddle portion 366, such that the center point of the auxiliary bone anchor opening 364 is offset laterally from the saddle portion and aligned with an inferior end of the saddle portion. In other embodiments, the auxiliary bone anchor opening 364 can be positioned approximately at a “3 o'clock” or “middle” position with respect to the saddle portion 366, such that the center point of the auxiliary bone anchor opening 364 is offset laterally from the saddle portion and aligned with a longitudinal midpoint of the saddle portion. In other embodiments, the auxiliary bone anchor opening 364 can be positioned approximately at a “1 o'clock” or “upper” position with respect to the saddle portion 366, such that the center point of the auxiliary bone anchor opening 364 is offset laterally from the saddle portion and aligned with a superior end of the saddle portion. A kit can be provided including a plurality of plates 360, each including auxiliary bone anchor openings 364 positioned at different locations with respect to the saddle portion 366, to give the user flexibility in locating the auxiliary bone anchor 334 relative to the rod 306. This can allow the user to select a plate 360 that will position the auxiliary bone anchor 334 in a good position to get bone purchase.

One or more portions of the plate 360 can be flexible or deformable to allow the plate to be custom-tailored for a particular situation. For example, as noted above, the portion of the plate 360 in which the bone anchor opening(s) 364 are formed can be bent or flexed to reposition said portion with respect to the portion of the plate in which the receiver member 304 is disposed. The plate 360 can be contoured before implantation or in situ. The plate 360 can be contoured using a separate bending instrument, or by tightening the bone anchors 334 to deform the plate into intimate contact with the bone surface. The plate 360 can be pre-shaped or pre-contoured, e.g., during manufacture, to match a bone surface or construct with which the bone anchor assembly 300 is to be used.

In some cases, the thickness of the saddle portion 366 can cause the spinal rod 306 to be raised up within the receiver member 304 to a degree that prevents sufficient attachment of the closure mechanism 308 or prevents attachment of the closure mechanism altogether. In such cases, the bone anchor assembly 300 can include a cap 372, e.g., of the type shown in FIG. 3H. The cap 372 can attach to the proximal end of the receiver member 304. The cap 372 can include a threaded central opening sized to receive the closure mechanism 308. Accordingly, the cap 372 can functionally extend the height of the threaded portion of the receiver member 304 to accommodate both the rod 306 and the saddle portion 366 between the rod-receiving channel of the receiver member 304 and the closure mechanism 308. The illustrated cap 372 includes a generally U-shaped channel sized to accommodate the spinal rod 306. The cap 372 can be attached to the receiver member 304 in any of a variety of ways. For example, the cap 372 can include one or more projections that engage with a corresponding one or more recesses formed in the receiver member 304, or the receiver member can include one or more projections that engage with a corresponding one or more recesses formed in the cap. The cap 372 can snap fit onto the receiver member 304. The cap 372 can slide onto the receiver member 304 from the side with a tongue and groove or dovetail connection. The cap 372 can lock onto the receiver member 304 by a quarter-turn rotation of the cap relative to the receiver member.

The bone anchor assembly 300 can provide significant flexibility for the surgeon. The plate 360 can be easily flipped around to be positioned on either side of the rod 306 (e.g., on a medial side or a lateral side of the rod). As described in detail above, the plate 360 can be deformable or flexible, or can include deformable or flexible portions, to allow the plate to fit snugly with the receiver member 304, to match a contour of the bone surface, to reposition the auxiliary bone anchor hole(s) 364 with respect to the receiver member, and/or to adjust a height of the plate to accommodate receiver members of different heights or situations where the primary bone anchor 302 is over or under inserted into the bone. The bone anchor assembly 300 is shown in FIG. 31 installed as part of a multi-level spinal fixation construct. As shown, the plate 360 allows an auxiliary bone anchor 334 to be installed at the same vertebral level as the primary bone anchor 302 to augment the fixation of the primary bone anchor.

Referring again to FIG. 3A, the proximal-most extent of each auxiliary bone anchor 334 can be distal to the spinal rod 306. In other embodiments, the proximal-most extent of each auxiliary bone anchor 334 can be distal to the distal-most extent of the receiver member 304. These configurations can advantageously reduce the overall profile of the assembly 300.

The centers of the auxiliary bone anchor hole(s) 364 (and thus at least a portion of the auxiliary bone anchor(s) 334 disposed therein) can be spaced radially apart from the center of the opening in the receiver member 304 in which the primary bone anchor 302 is disposed. In some embodiments, this spacing can be less than about 2.5 times the diameter of the receiver member 304. In some embodiments, this spacing can be less than about 2 times the diameter of the receiver member 304. In some embodiments, this spacing can be less than the diameter of the receiver member 304. In some embodiments, this spacing can be between about 5 mm and about 10 mm. In some embodiments, this spacing can be about 7.5 mm. In some embodiments, the auxiliary bone anchors 334 can be contained within an envelope no bigger than 2.5 times the diameter of the receiver member 304. In some embodiments, the auxiliary bone anchors 334 can be contained within an envelope no bigger than 2 times the diameter of the receiver member 304.

The auxiliary bone anchors 334 can include any of the features of the bone anchor 302 described above, and any of a variety of other bone screws or other anchors can be used instead or in addition. As noted above, the auxiliary bone anchors 334 can have threaded proximal heads to facilitate variable-angle locking with the plate 360. In some embodiments, the auxiliary bone anchors 334 can have a length of about 6 mm to about 20 mm (e.g., in embodiments used for cervical applications). In some embodiments, the auxiliary bone anchors 334 can have a length of about 6 mm to about 100 mm (e.g., in embodiments used for lumbar or sacral applications). The length of the auxiliary bone anchors 334 can be selected based on various factors, including the available safe bone at any given attachment location. The auxiliary bone anchors 334 can have a length equal to that of the primary bone anchor 302. The auxiliary bone anchors 334 can have a length less than that of the primary bone anchor 302. The auxiliary bone anchors 334 can have a length that is between about 60% and about 80% of the length of the primary bone anchor 302. The auxiliary bone anchors 334 can have a length that is about 70% of the length of the primary bone anchor 302. The auxiliary bone anchors 334 can have a length of about 10 mm. The auxiliary bone anchors 334 can have a length of about 14 mm. In some embodiments, two 10 mm auxiliary bone anchors can be used with one 14 mm primary bone anchor. In some embodiments, one 14 mm auxiliary bone anchor can be used with one 14 mm primary bone anchor. The auxiliary bone anchors 334 can have a shank diameter equal to that of the primary bone anchor 302. The auxiliary bone anchors 334 can have a shank diameter less than that of the primary bone anchor 302. The auxiliary bone anchors 334 can have a shank diameter that is between about 50% and about 70% of the shank diameter of the primary bone anchor 302. The auxiliary bone anchors 334 can have a shank diameter that is about 60% of the shank diameter of the primary bone anchor 302.

The saddle portion 366 can extend completely across the rod-receiving recess of the receiver member 304. The saddle portion 366 can extend across less than an entirety of the rod-receiving recess of the receiver member 304 (e.g., across only a portion of the rod-receiving recess). The saddle portion 366 can be omitted altogether. For example, the plate 360 can include an alternative distal facing portion to bear against the receiver member 304 and transfer the holding force of the auxiliary bone anchors 334 to the receiver member. Exemplary distal facing portions can include a lip, a shelf, a face, a tapered portion, and/or teeth that can mesh or engage with a portion of the receiver member 304.

FIGS. 4A-4E illustrate an exemplary embodiment of a bone anchor assembly 400, shown with a spinal rod 406. As shown, the bone anchor assembly 400 can include a bone anchor 402, a receiver member 404, a closure mechanism 408, a hook 474, a washer or collar 476, and a locking screw 478. In use, the collar 476 and locking screw 478 can be used to attach the hook 474 to the receiver member 404. The hook 474 can be hooked onto or engaged with a portion of the patient anatomy or a nearby implant to augment fixation of the bone anchor 402.

Except as described below or as will be readily appreciated by one having ordinary skill in the art, the bone anchor 402, receiver member 404, and closure mechanism 408 are substantially similar to the bone anchor 102, receiver member 104, and closure mechanism 108 described above. A detailed description of the structure and function thereof is thus omitted here for the sake of brevity. The bone anchor assembly 400 can include any one or more of the features of the bone anchor assembly 100 described above.

The hook 474 can include a body portion 480 with a curved or looped extension 482 projecting therefrom.

The extension 482 can be substantially U-shaped, with an inside curved surface 484 and an outside curved surface 486. The extension 482 can be sized and configured to hook onto a portion of the patient's anatomy (e.g., a lamina, spinous process, or other bone structure of the patient) or onto another implant or implant construct (e.g., a cross-connector, screw, rod, plate, intervertebral implant, or the like). For example, the inside curved surface 484 can form a negative or a substantial negative of the anatomy or implant.

As shown in FIG. 4A, the hook 474 can be coupled to the lamina L of the patient such that a proximal-facing surface 488 of the inside curve 484 of the extension 482 abuts a distal facing surface of the lamina and such that a distal-facing surface 490 of the inside curve 484 of the extension 482 abuts a proximal-facing surface of the lamina.

While a single extension 482 is shown in the illustrated embodiment, it will be appreciated that the hook 474 can include any number of extensions (e.g., one, two, three, four, five, and so on).

One or more portions of the hook 474 can be flexible or deformable to allow the hook to be custom-tailored for a particular situation. For example, the extension 482 of the hook 474 can be contoured to match the anatomy or implant onto which the extension is to be hooked. The hook 474 can be contoured before implantation or in situ. The hook 474 can be contoured using a separate bending instrument, or by tightening the locking screw 478 to deform the hook into intimate contact with the anatomy or implant. The hook 474 can be pre-shaped or pre-contoured, e.g., during manufacture, to match an anatomy or implant with which the bone anchor assembly 400 is to be used.

In some embodiments, a kit of modular hooks 474 can be provided to allow selection of the hook or hooks most appropriate for a given use. For example, hooks 474 having extensions 482 of varying sizes that correspond to the varying sizes of laminae found in a patient population or the varying sizes of laminae found within a single human spine can be included in the kit and the most appropriately sized hook can be selected for the surgery. Hooks 474 of varying size and/or varying offset relative to the receiver member 404 can be included in a kit.

The body portion 480 of the hook 474 can include an opening 492 for receiving the locking screw 478 to secure the hook to the collar 476. The opening 492 can be threaded such that the locking screw 478 can be threaded into the opening. The body portion 480 of the hook 474 can include a lateral surface 494 that engages a sidewall of the receiver member 404. The lateral surface 494 can form a negative of the sidewall of the receiver member 404, such that the hook 474 can hug the receiver member with minimal or zero gap therebetween. For example, the lateral surface 494 can be concave with a radius of curvature equal or substantially equal to a radius of curvature of the exterior sidewall of the receiver member 404.

The collar 476 can include a first opening 496A sized to receive at least a portion of the receiver member 404 therethrough and a second opening 496B sized to receive the locking screw 478 therethrough. The first and second openings 496A, 496B can intersect one another, such that the collar 476 defines a “snowman” or “figure eight” shaped central opening. The collar 476 can include one or more engagement features for forming a positive interlock with the receiver member 404, which can advantageously prevent the collar from inadvertently sliding off of the receiver member. For example, the collar 476 can include one or more projections 498 that extend radially inward into the first opening 496A to engage corresponding one or more recesses 499 formed in an exterior sidewall of the receiver member 404. In other embodiments, the recesses can be formed in the collar 476 and the projections can be formed on the receiver member 404. The first opening 496A can include one or more flats (e.g., opposed parallel, planar sidewalls as shown) that mate with corresponding one or more flats (e.g., opposed parallel, planar sidewalls) of the receiver member 404 to prevent rotation of the collar 476 with respect to the receiver member.

The second opening 496B of the collar 476 can be circular or semi-circular to accommodate the cylindrical shaft of the locking screw 478. In other embodiments, the second opening 496B can be elongated to allow the locking screw 478 to be secured at any of a variety of locations along a length of the elongated opening. This can advantageously allow the distance between the receiver member 404 and the hook 474 to be adjusted as desired. The second opening 496B can have a conical or tapered countersink shape as shown such that, as the locking screw 478 is tightened, the collar 476 is pushed to the right in FIG. 4A, cinching in the receiver member 404 and locking down the entire assembly.

When assembled, the collar 476 can sit above the spinal rod 406 and extend around the outer periphery of the receiver member 404 to secure the hook 474 to the side of the receiver member. The hook 474 can be hooked onto patient anatomy or another implant to augment the fixation of the bone anchor assembly 400. In some embodiments, the hook 474 can be hooked onto an anatomical structure at the same vertebral level as the bone anchor 402 is inserted. Thus, for example, the bone anchor 402 can be advanced into the pedicle or lateral mass of a vertebra and the hook 474 can be hooked onto a lamina of that same vertebra. As shown in FIG. 4A, the collar 476 does not interfere with insertion of the closure mechanism 408 into the receiver member 404, or with tightening or loosening of the closure mechanism. In addition, the hook 474 and collar 476 can be attached to the receiver member 404 after the rod 406 is installed in the receiver member.

The bone anchor assembly 400 can provide significant flexibility for the surgeon. The collar 476 and hook 474 can be easily flipped around to be positioned on either side of the rod 406 (e.g., on a medial side or a lateral side of the rod). The hook 474 can be deformable or flexible, or can include deformable or flexible portions, to allow the hook to fit snugly with the receiver member 404, to match a contour of the bone surface, to reposition the hook with respect to the receiver member, and/or to adjust a height of the hook to accommodate receiver members of different heights or situations where the primary bone anchor 402 is over or under inserted into the bone.

As shown in FIG. 4E, instead of using a locking screw 478 and a collar 476 that wraps around the receiver member 404, the hook 474 can attach to the receiver member in a manner similar to that used to attach the wing 230 of FIGS. 2A-2M. In particular, the hook can include a proximal portion 474 p that sits atop the opposed arms 414A, 414B of the receiver member 404 and that defines a central opening through which a closure mechanism 408 in the form of an extended threaded post is received. The hook 474 can be locked onto the closure mechanism 408 and the receiver member by a threaded nut 432.

The hook 474 can be attached to the receiver member 404 after the receiver member and the bone anchor 402 are coupled to the bone, which can advantageously give the surgeon more flexibility for insertion and also allow insertion of the bone anchor and receiver member with an unobstructed view. In addition, the hook 474 can be coupled to the receiver member 404 such that the bone anchor 402 does not restrict movement of the hook. The hook 474 can thus be positioned with respect to the bone anchor 402 at least with as many degrees of freedom as the receiver member 404.

An exemplary method of using the bone anchor assemblies disclosed herein is described below.

The procedure can begin by forming an open or percutaneous incision in the patient to access a bone in which a bone anchor assembly is to be implanted. The bone can be prepared to receive the bone anchor assembly as known in the art. For example, a pedicle of a vertebra can be prepared using standard awl, probe, and tap steps.

The bone anchor can then be advanced into the bone. If the user feels that the purchase of the bone anchor is inadequate, or that auxiliary fixation would otherwise be desirable, an auxiliary fixation member can be added to the bone anchor assembly.

For example, referring to the embodiment of FIGS. 2A-2M, a spinal rod 206 can be seated in the receiver member 204 and a closure mechanism 208 can be threaded down onto the rod. A wing 230 can then be positioned over the closure mechanism 208 and secured in place with the nut 232. One or more auxiliary bone anchors 234 can be inserted through the wing 230 to attach the construct to the bone at a second location (or at more than two locations). The method can include bending or flexing the wing 230 to better fit the receiver member 204 or bone surface, for example by squeezing legs 258 of the wing together to increase a height of the wing.

As another example, referring to the embodiment of FIGS. 3A-3I, a plate 360 can be seated in the receiver member 304 and a rod 306 can be positioned over the plate and secured to the receiver member using a closure mechanism 308. A cap 372 can be used if the height of the rod 306 and plate 360 exceeds the design height of the receiver member 304. One or more auxiliary bone anchors 334 can be inserted through the plate 360 to attach the construct to the bone at a second location (or at more than two locations). The method can include bending or flexing the plate 360 to better fit the receiver member 304 or bone surface.

As another example, referring to the embodiment of FIGS. 4A-4E, a spinal rod 406 can be seated in the receiver member 404 and a closure mechanism 408 can be threaded down onto the rod. A collar 476 can then be positioned over the receiver member 404 and secured to a hook 474 using a locking screw 478. The hook 474 can be hooked onto a portion of the patient's anatomy or a nearby implant to augment the fixation of the bone anchor assembly 400. The method can include bending or flexing the hook 474 to better fit the receiver member 404 or the anatomy or implant.

The above steps can be repeated to install additional bone anchor assemblies at the same or at different vertebral levels, with or without auxiliary fixation members. Final tightening or other adjustment of the construct can be performed and the procedure can be completed using known techniques and the incision closed.

In any of the above embodiments or methods, the primary bone anchor can be omitted and the user can rely solely on the one or more auxiliary fixation features to secure the bone anchor assembly. This can advantageously allow the position of the fixation to be completely offset from the receiver member, for example if an initially placed bone anchor needs to be removed due to improper positioning or inadequate purchase, or when the receiver member needs to be positioned over a location where a bone anchor cannot be inserted.

While the methods illustrated and described herein involve a bone anchor assembly placed in the pedicle or lateral mass of vertebral bone, it will be appreciated that the systems and methods herein can be used in any bone, in non-bone tissue, or in non-living or non-tissue objects.

The auxiliary fixation members disclosed herein can be implanted in the same surgical procedure as the bone anchor, receiver member, and spinal rod, or, in the case of revision surgery, during a subsequent surgical procedure.

It should be noted that any ordering of method steps expressed or implied in the description above or in the accompanying drawings is not to be construed as limiting the disclosed methods to performing the steps in that order. Rather, the various steps of each of the methods disclosed herein can be performed in any of a variety of sequences. In addition, as the described methods are merely exemplary embodiments, various other methods that include additional steps or include fewer steps are also within the scope of the present invention.

As evident from the foregoing, in at least some embodiments, the systems and methods disclosed herein can provide enhanced fixation for a given surgical site, providing greater bone fixation strength at a given location without necessarily requiring moving the fixation to an additional vertebra or skipping/increasing the involved vertebral levels.

The bone anchor assemblies disclosed herein and the various component parts thereof can be constructed from any of a variety of known materials. Exemplary materials include those which are suitable for use in surgical applications, including metals such as stainless steel, titanium, or alloys thereof, polymers such as PEEK, ceramics, carbon fiber, and so forth. The various components of the devices disclosed herein can be rigid or flexible. One or more components or portions of the device can be formed from a radiopaque material to facilitate visualization under fluoroscopy and other imaging techniques, or from a radiolucent material so as not to interfere with visualization of other structures. Exemplary radiolucent materials include carbon fiber and high-strength polymers.

The systems and methods disclosed herein can be used in minimally-invasive surgery and/or open surgery. While the systems and methods disclosed herein are generally described in the context spinal surgery, it will be appreciated that the systems and methods disclosed herein can be used with any human or animal implant, in any of a variety of surgeries performed on humans or animals, and/or in fields unrelated to implants or surgery.

Although specific embodiments are described above, it should be understood that numerous changes may be made within the spirit and scope of the concepts described. Accordingly, it is intended that this disclosure not be limited to the described embodiments, but that it have the full scope defined by the language of the following claims. 

1. A bone anchor assembly, comprising: a bone anchor; a receiver member coupled to a proximal end of the bone anchor and defining a recess configured to receive a rod; a closure mechanism threadably mated to the receiver member; a wing having a proximal portion disposed proximal to the receiver member, a distal portion that defines a bone anchor opening, and a spanning portion that connects the proximal and distal portions; and a nut configured to threadably engage the closure mechanism to secure the proximal portion of the wing to the proximal end of the receiver member.
 2. The assembly of claim 1, wherein the closure mechanism comprises a threaded post and wherein the wing includes an opening through which at least a portion of the threaded post is disposed.
 3. The assembly of claim 1, wherein the wing is rotatable about the closure mechanism.
 4. The assembly of claim 1, wherein a distal-facing surface of the proximal portion of the wing bears against a proximal terminal end of the receiver member.
 5. The assembly of claim 1, wherein a lateral surface of the distal portion of the wing forms a negative of a sidewall of the receiver member and wherein a lateral surface of the spanning portion of the wing forms a negative of a sidewall of the receiver member.
 6. The assembly of claim 1, wherein a lateral surface of the spanning portion of the wing includes a protrusion that engages a corresponding recess formed in the receiver member.
 7. The assembly of claim 1, wherein the spanning portion hugs the sidewall of the receiver member.
 8. The assembly of claim 1, wherein the receiver member is polyaxially movable relative to the bone anchor.
 9. The assembly of claim 1, further comprising an auxiliary bone anchor disposed in the bone anchor opening of the distal portion of the wing.
 10. The assembly of claim 9, wherein the proximal-most extent of the auxiliary bone anchor is distal to a rod when the rod is disposed in the recess of the receiver member.
 11. The assembly of claim 9, wherein the proximal-most extent of the auxiliary bone anchor is distal to the distal-most extent of the receiver member.
 12. The assembly of claim 1, wherein the spanning portion has an adjustable height.
 13. The assembly of claim 12, wherein the spanning portion comprises first and second legs movable toward one another to increase the height of the spanning portion and movable away from one another to decrease the height of the spanning portion.
 14. The assembly of claim 1, wherein the spanning portion is deformable to allow the distal portion of the wing to be angled to match an abutting bone surface.
 15. A method of securing a bone anchor assembly to bone, comprising: driving a bone anchor into bone, the bone anchor having a receiver member coupled to a proximal end thereof; positioning a rod in the receiver member; attaching a closure mechanism to the receiver member to retain the rod in the receiver member; coupling a proximal portion of a wing to at least one of the closure mechanism and a proximal surface of the receiver member; and inserting an auxiliary bone anchor through a bone anchor opening formed in a distal portion of the wing and driving the auxiliary bone anchor into the bone.
 16. The method of claim 15, wherein coupling the proximal portion of the wing comprises inserting at least a portion of the closure mechanism through an opening formed in the proximal portion of the wing.
 17. The method of claim 15, further comprising rotating the wing relative to receiver member to position the bone anchor opening of the wing with respect to a target location on the bone.
 18. The method of claim 15, further comprising deforming the wing to position the bone anchor opening of the wing with respect to a target location on the bone.
 19. The method of claim 15, further comprising adjusting a height of the wing such that the wing spans from the proximal-most extent of the receiver member to the bone.
 20. The method of claim 15, wherein the bone anchor and the auxiliary bone anchor are driven into a single vertebra.
 21. A bone anchor assembly, comprising: a bone anchor; a receiver member coupled to a proximal end of the bone anchor and defining a recess configured to receive a rod; a closure mechanism threadably mated to the receiver member; a plate having a primary opening through which first and second arms of the receiver member extend, a bone anchor opening, and a saddle portion that extends across at least a portion of the primary opening such that the saddle portion is disposed in the recess of the receiver member; and an auxiliary bone anchor disposed through the bone anchor opening of the plate.
 22. The assembly of claim 21, further comprising a rod disposed between the saddle portion of the plate and the closure mechanism.
 23. The assembly of claim 21, wherein the saddle portion is movably coupled to the plate.
 24. The assembly of claim 21, wherein a distal facing surface of the saddle portion forms a section of a cylinder.
 25. The assembly of claim 21, wherein the primary opening in the plate is defined by a first sidewall and wherein the bone anchor opening of the plate is defined by a second sidewall.
 26. The assembly of claim 25, wherein a height of the first sidewall is reduced where the first sidewall meets the second sidewall.
 27. The assembly of claim 21, further comprising a cap configured to engage the first and second arms of the receiver member and defining a central opening disposed proximal to a proximal-most extent of the receiver member, the central opening receiving at least a portion of the closure mechanism therethrough.
 28. The assembly of claim 21, wherein the proximal-most extent of the auxiliary bone anchor is distal to a rod when the rod is disposed in the recess of the receiver member.
 29. The assembly of claim 21, wherein the proximal-most extent of the auxiliary bone anchor is distal to the distal-most extent of the receiver member.
 30. A method of securing a bone anchor assembly to bone, comprising: driving a bone anchor into bone, the bone anchor having a receiver member coupled to a proximal end thereof; inserting first and second arms of the receiver member through a primary opening of a plate such that a saddle portion of the plate is disposed in a rod-receiving recess of the receiver member; positioning a rod on a proximal-facing surface of the saddle portion such that the rod is disposed in the rod-receiving recess of the receiver member; attaching a closure mechanism to the receiver member to retain the rod in the receiver member; and inserting an auxiliary bone anchor through a bone anchor opening formed in the plate and driving the auxiliary bone anchor into the bone.
 31. The method of claim 30, further comprising bending the plate to position the bone anchor opening against the bone.
 32. The method of claim 30, further comprising bending the saddle portion of the plate to position the bone anchor opening against the bone.
 33. The method of claim 30, wherein the bone anchor and the auxiliary bone anchor are driven into a single vertebra.
 34. A bone anchor assembly, comprising: a bone anchor; a receiver member coupled to a proximal end of the bone anchor and defining a recess configured to receive a rod; a closure mechanism threadably mated to the receiver member; a plate having a primary opening through which at least a portion of the receiver member extends, a bone anchor opening, and a distal-facing portion that extends across a proximal-facing portion of the receiver member; and an auxiliary bone anchor disposed through the bone anchor opening of the plate.
 35. A bone anchor assembly, comprising: a bone anchor; a receiver member coupled to a proximal end of the bone anchor and defining a recess configured to receive a rod; a closure mechanism threadably mated to the receiver member; and a hook having a body portion coupled to the receiver member and a curved extension projecting from the body portion.
 36. The assembly of claim 35, wherein the extension is substantially U-shaped and defines an inside curved surface and an outside curved surface.
 37. The assembly of claim 36, wherein the inside curved surface forms a substantial negative of a lamina.
 38. The assembly of claim 35, wherein the body portion has a lateral sidewall that abuts a sidewall of the receiver member.
 39. The assembly of claim 35, wherein the hook is coupled to the receiver member by a collar that defines a first opening in which the receiver member is disposed and a second opening through which a locking screw is disposed, the locking screw threadably engaging the body portion of the hook.
 40. The assembly of claim 39, wherein the first opening includes an engagement feature that engages a corresponding engagement feature formed in or on an exterior of the receiver member.
 41. The assembly of claim 39, wherein the second opening has a tapered shape to pull the receiver member towards the body portion as the locking screw is tightened.
 42. The assembly of claim 39, wherein the collar is disposed proximal to a rod when the rod is disposed in the receiver member.
 43. The assembly of claim 39, wherein the collar extends around an outer periphery of the receiver member.
 44. The assembly of claim 35, wherein the hook is configured to pivot with the receiver member relative to the bone anchor.
 45. The assembly of claim 35, wherein the hook is coupled to the receiver member by a nut threaded onto the closure mechanism to compress a proximal portion of the hook against a proximal end of the receiver member.
 46. A method of securing a bone anchor assembly to bone, comprising: driving a bone anchor into bone, the bone anchor having a receiver member coupled to a proximal end thereof; positioning a rod within a rod-receiving recess of the receiver member; attaching a hook to the receiver member and hooking an extension of the hook onto at least one of an anatomical structure and an implant; and attaching a closure mechanism to the receiver member to retain the rod in the receiver member.
 47. The method of claim 46, wherein the bone anchor is driven into a first vertebra and the extension of the hook is hooked onto a lamina of the first vertebra.
 48. The method of claim 46, wherein the hook is attached to the receiver member after the bone anchor is driven into the bone.
 49. The method of claim 46, wherein the closure mechanism is attached to the receiver member after the hook is attached to the receiver member.
 50. The method of claim 46, wherein the hook is attached to the receiver member after the rod is seated in the receiver member. 